1. Field of the Invention
The present invention generally relates to a circuit capable of driving electrical loads. The invention specifically described is a circuit that develops a commanded DC or AC signal from the high-frequency AC output voltage of a piezoelectric transformer.
2. Related Arts
A conventional power distribution circuit, as shown in FIG. 1a, steps-up and steps-down AC voltage via an electromagnetic transformer wherein primary and secondary windings are electromagnetically coupled to a magnetic core. Both windings and magnetic core limit miniaturization of such devices.
A conventional piezotransformer-based distribution circuit, as shown in FIG. 1b, also provides for voltage step-up and step-down. More specifically, a Rosen transformer excites a piezoelectric element at resonance frequency with an electrical input at one end of the element generating a mechanical vibration, thereafter converting mechanical vibrations into electrical voltage at a second end of the element. Piezoelectric transformers are smaller, lighter, and more efficient than conventional electromagnetic devices, however constrained to a limited operating frequency below that of electromagnetic transformers.
Higher frequency piezoelectric transformers are possible. Such devices achieve both higher operating frequency and higher power density than conventional Rosen transformers via a thickness extensional vibration mode. The resultant device operates at multiple voltage levels, since output voltage is dependent on the thickness ratio between individual layers along first and second ends of the piezoelectric element.
The output from a piezoelectric transformer has parallel capacitance and a capacitive load. Therefore, neither output nor load are directly switchable into the other except with an intervening element, typically an inductor to maintain efficiency. The related arts transform the high-frequency output from a piezoelectric transformer to DC voltage via a bridge rectifier and a fairly large capacitor. DC voltage is applied as a power supply for a switching amplifier to drive the load, again requiring a filter inductor, an inverter circuit and a feedback circuit.
Much of the complexity, bulk, and weight in the related arts is avoided by switching the high-frequency AC output from the piezoelectric transformer, also called the driving waveform, into the load at precisely the instant when the driving waveform crosses the present voltage value on the load and switching the load out when the driving waveform reaches the desired voltage. Thereafter, the switch is opened and the reactance of the load or an addition output capacitor element holds the voltage until the next switching cycle. A single bilateral switch is required.
An object of the present invention is to provide a smaller, lighter, and less complex circuit capable of driving electrical loads. A further object of the present invention is to provide a circuit capable of developing an AC voltage signal input from the high-frequency AC output of a piezoelectric transformer without capacitors or inverter.
The present invention is a drive circuit functionally distinct from conventional linear and switching drives and representing a new device called a trasversion or transconverter device. The invention is comprised of several high-frequency comparators and at least one bilateral switch. The invention converts one or more high-frequency output voltage signals from a piezoelectric transformer to low-frequency voltage signals, examples including but not limited to sinusoidal, sawtooth, ramp, and square waves, at the output amplitude voltage. The circuit switches a high-frequency AC voltage output from a piezoelectric transformer, also referred to as the driving waveform, into the load at precisely the instant when the driving waveform crosses the present voltage value on the load, and switches it out when the driving waveform reaches the desired voltage. Thereafter, the switch is opened and the reactance of the load or an additional output capacitor element holds the voltage until the next switching cycle. The circuit functions without inverter and regulation sections required in the related arts.
The circuit is applicable to various piezoelectric transformer sections wherein a high-voltage AC signal and a low-level supply are separately provided. For example, the present invention is applicable to a conventional piezoelectric transformer, a piezoelectric transformer coupling with high-level and low-level xe2x80x9cwindingxe2x80x9d outputs, and a dual piezoelectric transformer.
Several advantages are offered by the present invention. The invention is smaller, lighter, less costly, and more reliable than the related arts due to the elimination of iron core/ferrite transformer and amplifier. The invention eliminates large capacitors and invert section in the related arts. The invention is a modular design readily adaptable to a wide range of current-voltage output characteristics and waveforms. The invention generates an extremely low EMI/RFI signature and has a wide thermal excursion operating capability. The invention is widely applicable in such items as flourescent lighting systems, backlit lighting systems, computer electronics, and active materials and devices.